(Prior Art Statement)
Recently, organophosphorus compounds having an imidazolidinyl group have been investigated and developed. For instance, Japanese Unexamined Patent Publication No. She 61-267594 and Japanese Unexamined Patent Publication No. Hei 2-793 disclose that these compounds can be used as insecticides, acaricides, nematocides and agents for killing soil insect pests. However, these patents simply disclose organophosphorus compounds having an imidazolidine skeleton which carries an oxygen or sulfur atom on the 2-position. Moreover, the insecticidal, acaricidal and nematocidal effects of these compounds are insufficient and are not necessarily satisfactory.